Defect-mediated ionic hopping and green electricity generation in Al_2−xMg_xO₃-based hydroelectric cell

A direct evidence of enhanced water molecule splitting by increasing defect concentration in Al_2−xMg_xO₃ hydroelectric cells (HECs) has been elaborated for green electricity generation. Existence of F, F⁺ and [Mg]⁰ defect centers in nanoporous Al_2−xMg_xO₃ (x = 0–0.5) cell pellets has been confirmed by optical spectroscopy. Increased defect density from ~ 1.45 × 10¹⁵ cm⁻³ to 5.4 × 10¹⁶ cm⁻³ induced by increasing Mg doping concentration is found to be a key factor to control water molecule dissociation/splitting at alumina surface. Small polaron hopping-assisted ionic conduction for enhanced current density is analyzed by impedance spectroscopy. The maximum, 15 mA, current is obtained in Al_2−xMg_xO₃ HEC for x = 0.5 concentration resulting in 13.5 mW off-load peak output power as compared to 4.95 mW peak output power in pure alumina HEC. A theoretical modeling of Nyquist spectra analyzes ion–solid interaction for real charge transfer process in HEC. Deliberate defect creation in alumina devised for water molecule dissociation at room temperature paves the way to fabricate a facile green electricity generation source in the form of HEC. Al_2−xMg_xO₃-based hydroelectric cell is a very low-cost device to generate green electricity besides providing eco-friendly by-products without use of photocatalytic activity, acid/alkali or electrolyte. Moreover, presented innovative alumina-based HEC would be a big step for mitigating industrial waste consisting of alumina.

Graphic abstract

: Polaron assisted hopping of OH⁻ ions in the lattice of Al_2-xMg_xO₃ HEC and green electricity generation in the form of V-I plot.